Blanket for pyrolysis or drying of biomass

ABSTRACT

The disclosed embodiments are operable to produce biochar from a biomass or to dry a biomass through controlled heating. While prior art technologies are stationary enclosures, the embodiments provided herein are based on a portable, flexible laminated blanket that is draped over a biomass (e.g., a wood slash pile). In this way, the blanket functions as a portable and reusable kiln for pyrolyzing biomass into biochar or drying biomass.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/485,521, filed May 12, 2011, the disclosure of which is expresslyincorporated herein by reference in its entirety.

STATEMENT OF GOVERNMENT LICENSE RIGHTS

This invention was made with government support under DGE-0654252awarded by National Science Foundation. The government has certainrights in the invention.

BACKGROUND

In the United States, forestry activities produce over 80 million greentons of slash (wood waste) annually. Current forest practices requirethat this material be piled and either left in the forest to decomposeor burned. This wastes a potentially valuable renewable energy resourceand produces greenhouse gases like methane and CO₂.

Biochar production is an age-old technique that utilizes partialcombustion of a woody fuel source in an oxygen starved environment toconvert the rest of the wood to charcoal. Biochar is useful as arenewable energy feedstock, among other applications. Establishedbiochar production processes (e.g. the Missouri kiln, Brazilian beehivekiln, Slope type kiln) typically have the following features:

-   -   1. Wood is piled inside a large enclosure made of an air        impermeable material.    -   2. The wood inside is ignited producing heat.    -   3. Small holes in the enclosure provide air flow to feed a small        fire.    -   4. Heat produced from this fire is utilized to convert the        majority of the wood to biochar.    -   5. When all the wood is converted to biochar, the enclosure is        hermetically sealed and the charcoal allowed to cool until it is        safe to remove and utilize.

Due to increasing interest in renewable energy, improved methods forproducing biochar are of interest.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This summary is not intended to identify key features ofthe claimed subject matter, nor is it intended to be used as an aid indetermining the scope of the claimed subject matter.

In one aspect, a blanket is provided. In one embodiment, the blanketincludes a material having the following properties:

-   -   thermal insulation, such that the blanket is capable of        withstanding temperatures of from 100 to 1000 degrees C.;    -   gas impermeability; and    -   flexibility, such that the blanket can be folded over on itself        for storage;    -   wherein the blanket is configured to conformally cover a        combusting biomass to facilitate pyrolysis or drying of the        biomass.

The combination of these properties is unique because it provides almostidentical functionality as the brick and mortar used in stationarykilns, but because the material is flexible it provides a means toeconomically convert remote slash piles (e.g., at logging sites) intobiochar.

In another aspect, a method is provided to produce biochar or drybiomass. In one embodiment, the method includes the steps of:

(a) combusting a biomass at a temperature sufficient to initiatepyrolysis or drying of the biomass;

(b) covering the biomass with a blanket as disclosed herein, wherein thetemperature of the biomass covered by the blanket can be controlled andis sufficient to pyrolize or dry the biomass, and wherein air fromoutside the blanket only reaches the biomass in a controlled manner; and

(c) maintaining the temperature of the biomass covered by the blanketfor a sufficient time to produce biochar or dry biomass.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of a representative blanket coveringa combusting biomass in accordance with aspects of the presentdisclosure;

FIGS. 2-4 are schematic illustrations of representative blankets inaccordance with aspects of the present disclosure;

FIG. 5 is a schematic illustration of air flow and heat movement inrelation to a representative blanket covering a combusting biomass inaccordance with aspects of the present disclosure;

FIG. 6 is a theoretical temperature profile through a thickness of arepresentative blanket from a hot side near a combusting biomass to acool side furthest from the combusting biomass in accordance withaspects of the present disclosure;

FIG. 7 is a photograph of an exemplary blanket having three layers inaccordance with aspects of the present disclosure; and

FIGS. 8A and 8B are visual (8A) and thermal (8B) images of arepresentative blanket covering a combusting biomass in accordance withaspects of the present disclosure.

DETAILED DESCRIPTION

The disclosed embodiments are operable to produce biochar from a biomassor to dry a biomass through controlled heating. While prior arttechnologies are stationary enclosures, the embodiments provided hereinare based on a portable, flexible laminated blanket that is draped overa biomass (e.g., a wood slash pile). In this way, the blanket functionsas a portable and reusable kiln for pyrolyzing biomass into biochar ordrying biomass. As used herein, the term “biomass” refers to any biomassknown to those of skill in the art, and includes naturally occurringcarbon sources.

In one aspect, a blanket is provided. In one embodiment, the blanketincludes a material having the following properties:

-   -   thermal insulation, such that the blanket is capable of        withstanding temperatures of from 100 to 1000 degrees C.;    -   gas impermeability; and    -   flexibility, such that the blanket can be folded over on itself        for storage;    -   wherein the blanket is configured to conformally cover a        combusting biomass to facilitate pyrolysis or drying of the        biomass.

The combination of these properties is unique because it provides almostidentical functionality as the brick and mortar used in stationarykilns, but because the material is flexible it provides a means toeconomically convert remote slash piles (e.g., at logging sites) intobiochar.

Referring now to FIG. 1, a representative blanket 105 is schematicallyillustrated covering a combusting biomass 110 resting on a surface 115(e.g., dirt). The blanket 105 can be any blanket having the above-listedproperties. Various embodiments of the blanket 105 are described furtherbelow.

So as to contain the thermal energy of the combusting biomass 110, theblanket 105 is a thermal insulator. The combusting biomass 110 may havea temperature of from 100 to 1000 degrees C., and in certain embodimentsthe blanket 105 withstands heat (i.e., maintains structural stability)across this range. In other embodiments, the blanket 105 is capable ofwithstanding temperatures of from 200° C. to 650° C. (e.g., forpyrolyzing biomass). In other embodiments, the blanket 105 is capable ofwithstanding temperatures of from 100° C. to 250° C. (e.g., for dryingbiomass).

The blanket 105 is also gas impermeable so as to prevent combustion fuelgasses to diffuse through the blanket 105. As used herein, the term “gasimpermeable” defines a material that allows negligible oxygen diffusionthrough its thickness. By preventing gas diffusion, and particularlyoxygen diffusion, the blanket 105 limits fuel to the combusting biomass110 covered by the blanket 105. Because oxygen cannot pass through theblanket 105, the only oxygen provided to the combusting biomass mustpass around the blanket 105. However, in one embodiment, a plurality ofair vents 120 (see FIG. 5) are disposed peripherally on the blanket 105,wherein the plurality of air vents are configured to providecontrollable air flow to pyrolyzing or drying biomass disposed beneaththe blanket. The air vents 120 are positioned in the blanket 105 toprovide controllable air flow to the combusting biomass 110. Bycontrolling the flow of oxygen to the combusting biomass 110, theblanket 105 allows a user to pyrolize the biomass into biochar insteadof combusting it into ash. In one embodiment, air from outside theblanket only reaches the biomass by passing around the periphery of theblanket.

The blanket 105 is also flexible, such that it can be folded over onitself for storage. By being flexible, it can be transported easily soas to facilitate pyrolysis of biomass in remote locations, such aslogging sites and the like. Flexibility also allows the blanket 105 toconformally cover a combusting biomass 110. This allows the headspacebetween the blanket 105 and the combusting biomass 110 to be minimized,which facilitates pyrolysis and generally allows a user to control thetemperature of the combusting biomass 110.

While the figures herein generally refer to use of the blanket 105 foruse in pyrolysis of a biomass, it will be appreciated that the blanket105 can similarly be used to dry the biomass, if the temperature iscontrolled properly, as will be discussed in more detail below.

Biomass drying is accelerated as the temperature of the biomass iselevated. Control of the oxygen flow under the blanket (e.g., via vent)can enable a small amount of combustion heat, to warm the biomasswithout pyrolysis, by restricting the oxygen input below that needed tosustain pyrolysis. Under these conditions, the blanket enables the warmcombustions gases to circulate prior to exiting the blanket, therebyraising the temperature of the biomass. All but the most tightly boundwater (generally less than 10% by weight) is liberated from the biomassas the temperature approaches 100° C., the boiling point of water.

Referring now to FIG. 2, in one embodiment, the blanket 105 consists ofa single layer 205 having all of the required properties. The blanket105 will have a “hot” side nearest the combusting biomass 110, and a“cool” side furthest from the combusting biomass 110.

In one embodiment, the blanket comprises a thermal insulation layercapable of withstanding temperatures of from 100 to 1000 degrees C.; anda gas impermeable layer that is a different material than the thermalinsulation layer, wherein the thermal insulation layer is disposedcloser to the combusting biomass than the gas impermeable layer.

Referring now to FIG. 3, the blanket 105 comprises two layers: A thermalinsulation layer 305, on the hot side, and a gas impermeable layer 310on the cool side. The combination of the two layers (305 and 310)provides all of the required properties.

In one embodiment, the thermal insulation layer 305 comprises a ceramicmaterial. In one embodiment, the ceramic material is selected from thegroup consisting of ceramic pressed particulate paper and woven ceramicfibers (e.g., basalt).

In one embodiment, the gas impermeable layer 310 is a metal foil. In oneembodiment, the metal foil is selected from the group consisting ofstainless steel foil, aluminum foil, or other refractory metals andalloys foils from them.

In one embodiment, the blanket has the additional property ofdurability, such that the blanket is not structurally damaged afterrepeated exposure to temperatures of from 100 to 1000 degrees C.Referring now to FIG. 4, a three (or more) layer blanket 105 isprovided. In addition to the thermal insulation layer 305 and the gasimpermeable layer 310 described with reference to FIG. 3, a firstprotective layer 410 is provided that confers the property ofdurability. The first protective layer 410 is disposed closest to thecombusting biomass 110.

The protective layer 410 protects any of the other layers of the blanket105 from being compromised (e.g., by ripping or puncturing) while inuse. This is particularly desirable if the thermal insulation layer 305is a ceramic material, which are typically fragile. Small holes in theblanket can serve as nucleation sites for larger tears and rips to form,which reduces reusability of the blanket. In one embodiment, the firstprotective layer is a metal mesh layer. In a further embodiment, themetal mesh layer is a stainless-steel mesh layer.

An optional second protective layer 415 can be added to providedurability to both the hot and cool sides of the blanket 105 for maximumdurability. The second protective layer 415 can be the same or differentin composition as the first protective layer 410.

In another aspect, a method is provided to produce biochar or drybiomass. In one embodiment, the method includes the steps of:

(a) combusting a biomass at a temperature sufficient to initiatepyrolysis or drying of the biomass;

(b) covering the biomass with a blanket as disclosed herein, wherein thetemperature of the biomass covered by the blanket can be controlled andis sufficient to pyrolize or dry the biomass, and wherein air fromoutside the blanket only reaches the biomass in a controlled manner; and

(c) maintaining the temperature of the biomass covered by the blanketfor a sufficient time to produce biochar or dry biomass.

In one embodiment, the biomass is pyrolized at a temperature of fromabout 200° C. to 650° C. In one embodiment, the biomass is dried at atemperature of from about 100° C. to 250° C.

In one embodiment, the step of maintaining the temperature of thebiomass covered by the blanket for a sufficient time to produce biocharor dry biomass comprises adjusting the amount of air flowing to thebiomass at least once.

In one embodiment, adjusting the amount of air flowing to the biomasscomprises moving a peripheral edge of the blanket to increase ordecrease airflow or operating peripheral vent ports.

The following example is provided for the purpose of illustrating, notlimiting, the disclosed embodiments.

EXAMPLE Development and Testing of Pyrolysis Blanket

The experimental development of a representative pyrolysis blanket willnow be described. The primary goal during development was to create aportable, reusable mechanism for pyrolyzing biomass.

The first prototype was a semipermeable ceramic material. The blanketprovided multiple functions: (1) Capture and redistribute heat generatedin the local regions of combustions, and (2) permit hot volatile off-gasto vent slowly out of the pile.

The blanket was made from a high-temperature semi-permeable ceramicfiber blanket material. This material is by its very nature a very goodinsulator because it is made of woven basalt fibers, which have a lowthermal conductivity. The gas permeability of the blanket was alsowithin a range that was expected to be functionally appropriate for thescale of the biomass pile that was targeted for pyrolysis (200 lbs ofgreen wood).

During the progress of the burn the temperature under the blanketreached as high as 450° C., a temperature indicating that a significantamount of combustion was occurring. Another critical finding was thatbecause of the semipermeable air barrier, combustion could not bereduced over time. Therefore, as more and more charcoal was produced, itwas being combusted. Removing the blanket only caused the charcoal toignite, effectively degrading our desired product, biochar.

One issue was the difference in max temperature between the coveredpile, 750° F. versus the uncovered pile 1050° C. This is strong evidencethat the blanket is serving to limit some of the combustion, but notenough toward the end of the process to affect efficient charcoalrecovery.

There were a number of significant insights gleaned from the firstprototype that are summarized below:

-   -   1. The combustion of wood locally in a pile is sufficient to        carbonize even large diameter wood as long as the heat is        captured and redistributed.    -   2. A semi-permeable barrier is effective at suppressing        combustion but not easily sealed when the wood is done        carbonizing and the process needs to be “shut-off” such that the        biochar can be collected.    -   3. Free convection of volatile/heated gases is a significant        factor in design of inlets and outlets and providing heat        throughout the pile to affect wood conversion.

While the design recommendations above suggested that the semipermeableblanket system was not sufficient for large pile conversion, we wereable to use it effectively to produce high quality charcoal on a smallscale. Some modifications to the blanket to improve durability andcontrol over the temperature within the blanket were made for a secondprototype.

The other major change that was made involved the insertion of an outletinto the top of the blanket. This was to improve the rate of volatilerelease created during the biochar production process. This simpledesign was hypothesized to provide a means to control the temperature bychanging the outlet diameter.

Testing of the second prototype required manually tuning the diameter ofthe outlet in order to control the temperature within the blanket. Whilethis is not realistic on a large scale, this demonstrated that theoutlet diameter had a strong influence over the temperature and thatwith appropriate outlet size, the temperature could be varied from 250°C. up to 650° C. reproducibly with 20° C. accuracy. This temperaturespans the relevant range to achieve biochar with different propertiesfor various applications.

There were a number of significant insights gleaned from the secondprototype that are summarized below:

-   -   1. Orifice diameter should be something that is controllable        because as more biochar is produced, it needs to be adjusted to        maintain a constant temperature within the pile.    -   2. A semi-permeable barrier is not suitable to produce biochar        on a large scale because its combustion cannot be effectively        stopped.    -   3. Metal mesh is effective at providing durability and added        structure to the blanket to make more complicated geometries        over the wood possible.

After critical evaluation of the requirements of scale, several changeswere made to the blanket and operational design to achieve the finalprototype. The first change was to incorporate a metal foil into thelaminate. This foil serves to reflect radiative heat, but mostimportantly, provides an air impermeable layer behind the ceramic fiberinsulation to stop permeation of air through the blanket. This laminatedesign is shown in FIGS. 4 and 7. In the third prototype, the foil isplaced such that it is on the cool side of the blanket as its meltingpoint is rather low compared to the expected operating temperatures.

Implementing the impermeable layer is critical to the ability to mediatetemperature under the blanket, but also to recovering the biochar afterthe pyrolysis is completed. Without this layer, air will continuallypermeate into the biochar, potentially maintaining sufficient combustionto lose the entire product if not actively quenched. The use of animpermeable material also required reconsideration of how to controlairflow into the pile. In this regard, controllable inlets and outletswere been placed radially around the blankets bottom in order to drivethe buoyant convection that results in good mixing within the pile. Asimple schematic of this design is shown in FIG. 5.

The blanket has good thermal performance and gas impermeability. FIG. 6is a theoretical temperature profile through a thickness of arepresentative blanket from a hot side near a combusting biomass to acool side furthest from the combusting biomass in accordance withaspects of the present disclosure.

FIG. 7 is a photograph of an exemplary blanket having three layers: aceramic fiber thermal insulation layer, an aluminum foil gas impermeablelayer, and a stainless steel mesh protective layer.

Tests of the blanket of FIG. 7 successfully demonstrated a blanketsystem that possesses the necessary features to produce biochar in ascalable and inexpensive manner. The blanket is flexible andinexpensive, can be simply lain over an existing wood pile once a fireis ignited in order to convert the rest of the wood to biochar. Inletsand outlets have been integrated into the blanket which can control airflow and thus temperature inside the pile dynamically. The blanketsurvived testing with minimal wear. The blanket can be formed to anysize, including larger sizes to accommodate larger piles of biomass.Pictures of the blanket field test are shown in FIGS. 8A and 8B, whichare visual (8A) and thermal (8B) images of a representative blanketcovering a combusting biomass. Note that the thermal image in FIG. 8Bregisters a temperature of 166° C. on the cool side of the blanket,indicating a relatively low temperature (estimated to be about 300° C.)on the hot side of the blanket, which is conducive to pyrolysis of thebiomass into biochar.

While illustrative embodiments have been illustrated and described, itwill be appreciated that various changes can be made therein withoutdeparting from the spirit and scope of the invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A blanket comprising amaterial having the following properties: thermal insulation, such thatthe blanket is capable of withstanding temperatures of from 100 to 1000degrees C.; gas impermeability; and flexibility, such that the blanketcan be folded over on itself for storage; wherein the blanket isconfigured to conformally cover a combusting biomass to facilitatepyrolysis or drying of the biomass.
 2. The blanket of claim 1, whereinthe blanket consists of a single layer.
 3. The blanket of claim 1,wherein the blanket comprises two or more layers.
 4. The blanket ofclaim 3, wherein the blanket comprises a thermal insulation layercapable of withstanding temperatures of from 100 to 1000 degrees C.; anda gas impermeable layer that is a different material than the thermalinsulation layer, wherein the thermal insulation layer is disposedcloser to the combusting biomass than the gas impermeable layer.
 5. Theblanket of claim 3, wherein the thermal insulation layer comprises aceramic material.
 6. The blanket of claim 5, wherein the ceramicmaterial is selected from the group consisting of ceramic pressedparticulate paper and woven ceramic fibers.
 7. The blanket of claim 3,wherein the gas impermeable layer is a metal foil.
 8. The blanket ofclaim 7, wherein the metal foil is selected from the group consisting ofstainless steel foil or other refractory metals and alloys foils fromthem.
 9. The blanket of claim 1, wherein the blanket has the additionalproperty of durability, such that the blanket is not structurallydamaged after repeated exposure to temperatures of from 100 to 1000degrees C.
 10. The blanket of claim 9, wherein the blanket furthercomprises a first protective layer that confers the property ofdurability, wherein the first protective layer is disposed closest tothe combusting biomass.
 11. The blanket of claim 9, wherein the firstprotective layer is a metal mesh layer.
 12. The blanket of claim 9,wherein the metal mesh layer is a stainless-steel mesh layer.
 13. Theblanket of claim 9, wherein the blanket further comprises a secondprotective layer, disposed furthest from the combusting biomass.
 14. Theblanket of claim 1, further comprising a plurality of air vents disposedperipherally on the blanket, wherein the plurality of air vents areconfigured to provide controllable air flow to pyrolyzing or dryingbiomass disposed beneath the blanket.
 15. A method, comprising the stepsof: (a) combusting a biomass at a temperature sufficient to initiatepyrolysis or drying of the biomass; (b) covering the biomass with theblanket of any one of claims 1-14, wherein the temperature of thebiomass covered by the blanket can be controlled and is sufficient topyrolize or dry the biomass, and wherein air from outside the blanketonly reaches the biomass in a controlled manner; and (c) maintaining thetemperature of the biomass covered by the blanket for a sufficient timeto produce biochar or dry biomass.
 16. The method of claim 15, whereinthe biomass is pyrolized at a temperature of from about 200° C. to 650°C.
 17. The method of claim 15, wherein the biomass is dried at atemperature of from about 100° C. to 250° C.
 18. The method of claim 15,wherein the step of maintaining the temperature of the biomass coveredby the blanket for a sufficient time to produce biochar or dry biomasscomprises adjusting the amount of air flowing to the biomass at leastonce.
 19. The method of claim 18, wherein adjusting the amount of airflowing to the biomass comprises moving a peripheral edge of the blanketto increase or decrease airflow or operating peripheral vent ports. 20.The method of claim 15, wherein air from outside the blanket onlyreaches the biomass by passing around the periphery of the blanket.